Terry catches a ray-finned fish from the ocean and notices that, attached to its flank, there is an equally long, snakelike organism. The attached organism has no external segmentation, no scales, a round mouth surrounded by a sucker and two small eyes. Terry thinks it might be a marine leech, a hagfish, or a lamprey.

Which feature excludes it from possibly being a leech?
A) its elongate shape
B) its lack of external segmentation
C) its round mouth
D) its lack of scales
E) its anterior sucker